Methods and apparatus for applying powder coatings to articles



United States Patent [72] Inventor Neil Rudolph Wallis Cariad,Goring-on-Thames, Oxfordshire,

, England I [211 App]. No. 666,359 [22] Filed Sept. 8, 1967 [45]Patented Dec. 29, 1970 I [32] Priority Sept. 8, 1966 i [33] GreatBritain [31 40,152/66 [54] METHODS AND APPARATUS FOR APPLYING POWDERCOATINGS T0 ARTICLES 13 Claims, 4 Drawing Figs.

[52] US. Cl 239/15, 239/3 [51] Int. Cl B05b 5/00 [50] Field ofSearch239/3, 15, 561

[56] References Cited UNITED STATES PATENTS 2,685,536 8/1954 Starkey etal. 239/3X 2,794,417 6 1957 Starkeyetal. 239/15x 2,855,245 10/1958Sedlacsik,Jr 239/15 3,156,292 11/1964 Ross 239/56] FOREIGN PATENTS1,504,900 10/1967 France 239/15 l,529,187 5/1968 France 239 15 PrimaryExaminer-Lloyd L. King Assistant ExaminerThomas C. Culp, Jr.Att0rneyShoemaker and Mattare ABSTRACT: An apparatus for applying powdercoating material to an article comprising an elongate tubular member ofinsulating material having a plurality of holes opening directly througha wall thereof to the atmosphere and including a plurality of electrodeslocated wholly within the hollow member and disposed in the vicinity ofthe hole in the wall of said member and means for maintaining anelectrostatic field between said electrodes and an article to be coated.

PATENTEDnEc29|9m I 3.550.552

NEIL RMDOl-PH KAI/951.413

METHODS AND APPARATUS FOR APPLYING POWDER COATINGS TO ARTICLES Thisinvention relates to apparatus for applying powder coating material toarticles and it is an object of the invention to provide simpleapparatus which is effective to apply powder to articles under theinfluence of an electrostatic field.

The invention consists in apparatus for applying powder coating materialto an article, including a perforated hollow member of insulatingmaterial, means for supplying coating material to the interior of saidhollow member, a plurality of electrodes located within said hollowmember each in the vicinity of a hole in the wall of said member, andmeans for maintaining an electrostatic field between said electrodes andsaid article.

The invention also consists in a method of applying powder coatingmaterial to an article, wherein coating material is supplied to theinterior of an elongated. perforated hollow member of insulatingmaterial and is caused to leave said hollow member through theperforations therein under the influence of an electrostatic fieldmaintained between said article and a plurality of electrodes locatedwithin said hollow member, each in the vicinity of a perforation in thehollow member.

Preferably the hollow member has a circular cross section and isgenerally in the form of a length of pipe. In some instances, the pipemay be straight, but in other instances it may be curved. When thehollow member is generally cylindrical, the coating material ispreferably supplied to the interior of the hollow member at one endthereof, butwhen the hollow member is in the form of a curved pipe, thematerial may be supplied to the interior of the hollow member, forexample, at its midpoint or at two or more positions symmetricallyarranged with respect to the midpoint.

The electrodes are preferably supported by a metallic support memberwhich extends along the length of the hollow member and is connected toone terminal of a DC high-voltage source, the other terminal of which isconnected to the article to be coated. I

Methods of performing the invention will now be described with referenceto the accompanying diagrammatic drawings in which:

FIG. I is a sectional side view of one embodiment of the invention;

FIG. 2 is aside view of a second embodiment of the invention;

FIG. 3 is an end view of the front part of the embodiment illustrated inFIG. 2; and

FIG. 4 is a plan view of the part illustrated in'FlG. 3.

In the embodiment illustrated in FIG. 1', the perforated hollow memberis in the form of a straight length of pipe 1, having a row of holes 2spaced along its length. One end of the pipe is closed by means of aplug 3 and a rod support member 4 passes through the plug 3. The rod 4is supported within the pipe 1 by means not shown, and it will be seenthat it is located at a position which is displaced from thelongitudinal axis of the tube and is diametrically opposite to the rowof holes 2. A plurality of pointed electrodes 5 are secured to the rod 4opposite respective ones of said holes and the rod 4 is connected to oneterminal of a DC high-voltage source, the other terminal of which isconnected to the article to be coated, and preferably also to earth. Theelectrodes 5 may consist of metal, but preferably consist of nyloncoatedwith a mixture of carbon and resin. At the open end of the pipe 1,a conduit 6 is provided for the introduction of powder material into thepipe. The cross-sectional area of the conduit 6 is less than thecross-sectional area of the pipe 1 and may be, for example, one quarterof the cross-sectional area of the pipe.

Preferably, the powder coating material is transported along the conduit6 in the form of a suspension of powder in air. The suspension of powderin the conduit 6 may be formed, for example, in the manner described inmy copending application No. 651,025 filed 3rd July, 1967.

It will be seen that the electrodes 5 are pointed and that the pointsare arranged slightly nearer to the inlet end of the pipe 1 than thecenters of the corresponding holes 2. This arrangement will allow thepowder particles to follow a curved path after being deflected by theelectrostatic field and hence will ensure that the maximum amount ofpowder is ejected from the holes. The points of the electrodes 5 willnormally extend slightly beyond the median plane of the pipe 1, but toassist in the even distribution of the powder from the various holes,the electrodes remote from the inlet end of the pipe may be caused toproject further than those at the inlet end. In the embodimentillustrated, this arrangement is achieved by using electrodes ofincreasing length, but in an alternative embodiment, the supportelectrode 4 is mounted at an angle to the median plane of the pipe. Toenable adjustments to be made easily, it may be desirable to mount thesupport member on threaded pillars which can be moved inwardly andoutwardly from the outside of the pipe. Alternatively, or in addition,if

the support member is in the form of a metal bar, it may be threaded atsuccessive points along its length enabling the pointed electrodes to beadjustably mounted therein.

When the shape of the articles to be coated is irregular, it may bedesirable to use a curved pipe rather than a straight one. However, inthis case, care must be taken to ensure that the radius of curvature ofany bends in the pipe is suff ciently great in relation to the velocityof the powder to prevent the powder from being deflected under theaction of centrifugal force towards the outside of the bend, unless, ofcourse, the row of holes is located on the outside of the bend.

In certain circumstances, the flow pattern of the powder may be improvedby changingthe diameter of the pipe along its length to cause anincrease or decrease in the velocity of the powder travelling along theinterior of the pipe.

In the embodiment of the invention illustrated in FIGS. 2, 3 and 4, thestraight length of pipe I is replaced by a horseshoeshaped length ofpipe 11. The length of pipe 11 is mounted by means not shown at the endof the barrel 12 of a manual powder coating gun. A handle 13 is securedtqthe barrel 12 by means of a clamp 14 and the apparatus is controlledby means of a trigger 15. A suspension of powder coating material in airis supplied to the coating apparatus by means of a conduit 16 which isconnected to the horseshoe-shaped pipe 11 by means of a bifurcated joint17 visible in FIG. 4. The joint 17 opens into the pipe 11 at two pointssymmetrically placed with respect to the plane of symmetry of thehorseshoe. A support member 24 is mounted inside the pipe 11 and extendsfrom one end of the horseshoe to the other. A plurality of pointedelectrodes 25 are fitted into the support member 24 and each electrodeis located opposite a respective one of a series of holes 22 provided inthe front face of the horseshoe. A highvoltage cable 18 extends throughthe barrel l2 and is electrically connected to the support member 24 bymeans of a flexible connector 19. Preferably, this connector hassemiconductive properties and may, for example, consist of nylon threadsimpregnated with a mixture of rubber and carbon.

When the apparatus is in use, the conduit 16 is connected to apparatusfor forming a suspension of powder coating material in air and thehigh-voltage cable 18 is connected to one terminal of a DC source, theother terminal of which is connected to the article to be coated.Control leads (not shown) extend from microswitches controlled by thetrigger 15 to the suspension-forming apparatus and to the high-voltagesource, so that the operation of;the gun can be controlled by means ofthe trigger 15. It is to be understood that the powder particles leavethe apparatus through the holes 22 under the influence of theelectrostatic field between the electrodes 25 and the article to becoated. Since the particles are charged, they will travel to, and bedeposited on, the article tobe coated. Provided the quantity of air usedto transport the powder along the conduit 16 is not excessive, the aircan leave the apparatus also through the holes 22 without disturbing thedeposition of powder on the article to be coated. However, if an excessquantity of air is present, it will be found desirable to leave the freeends of the pipe 11 open so that air can leave through these ends of thepipe. Provided the total area of the holes 22 is large enough for allthe powder to leave therethrough, there should be no powder left at thefree ends of the pipe and accordingly only air will be discharged atthese points.

'Whilst the invention has been hereinbefore described as apparatus forapplying powder coating material to articles, it will be appreciatedthat it may also be used for separating suspended matter from a fluid.If, for example, dust-laden air is introduced into the embodimentillustrated in FIG. 1 through the conduit 6, and if the plug 3 isremoved from the far end of the pipe 1, substantially all the dust willleave through the holes 2 and clean air will be discharged through thefar end of the pipe. The cleanliness of the air leaving the pipe isdependent on the length of the pipe and the size and number of the holes2. However, provided the length of the pipe is sufficient in relation tothe velocity of the suspended matter through the pipe, substantially nosuspended matter will reach the far end of the pipe. it is to beunderstood that a receiving electrode must be provided in thisarrangement opposite the holes 2, and since it may, in'sorne instances,be convehient to use a cylindrical receiving electrode, the supportmember 4 may be provided on the axis of the pipe 1 and holes 2 may beprovided at a plurality of different circumferential positions aroundthe pipe 1 instead of being arranged in a single row as illustrated inFIG. 1.

lclaim:

1. Apparatus for applying powder coating material to an article,including a hollow elongate member of insulating material, a wall ofsaid member having a plurality of holes therein opening directly to theatmosphere, means for supplying coating material to the interior of saidhollow member, a pliirality of electrodes located wholly within saidhollow member each in the vicinity of a hole in the wall of said member,and means for maintaining an electrostatic field between said electrodesand said article.

2. Apparatus as claimed in claim 1, wherein said hollow member isgenerally cylindrical, and wherein the coating material is supplied tothe interior of the hollow member at one end thereof.

3. Apparatus as claimed in claim 1, wherein said hollow member is in theform of a curved pipe.

4. Apparatus as claimed in claim 3, wherein the coating material issupplied to the interior of the hollow member at a plurality of pointsintermediate the ends thereof.

5. Apparatus as claimed in claim 1, wherein the pluralityof holes arespaced along the length of the hollow member.

6. Apparatus as claimed in claim 5, wherein said electrodes aresupported by a support member connected to one terminal of a DChigh-voltage source,,'the other terminal of which is adapted to beconnected to the article to be coated.

7. Apparatus as claimed in claim 6, whereinthe electrodes are pointedand are secured to said support member opposite respective ones of saidholes. 7 p

8. Apparatus as claimed in claim 1, wherein the diameter of the-holesinthe hollow member increases along the length of the hollow member fromthe point or points at which the coating material is introduced into theinterior thereof.

9. Apparatus as claimed in claim 1, wherein the powder coating materialis supplied to the hollow member as a suspension in air by means of aconduit, the cross-se ctional area of which is less than thecross-sectional area of the hollow member.

10. Apparatus as claimed in claim 1, wherein each electrode powder inletincreases.

13. A method of applying powder coating to an article,

wherein coating material is supplied to the interior of an elongatedperforated hollow member of insulating material and is caused to leavesaid hollow member through the perforations therein under the influenceof an electrostatic field maintained between said articles and aplurality of electrodes located within said hollow member, each in thevicinity of a perforation in the hollow member.

